Heretofore, photographic processes using silver halide have been most widely practiced for general photographic purposes, since they provide excellent sensitivity, gradation, and like photographic properties as compared, for example, with electrophotographic process and diazo-type photographic process. In recent years, techniques have been developed which provide images easily in a short time by employing, as a photographic development process for forming images on light-sensitive materials using silver halide, a dry processing involving heating in place of the conventional wet processing involving development in a developing solution.
Heat developable light-sensitive materials are known in the art, and heat developable light-sensitive materials and the process thereof are described, for example, in Shashin-Kogyo no Kiso (The Foundations of Photographic Technology), Corona Co., pp. 553 to 555 (1979); Eizo Joho, April 1978, p. 40; Nebletts Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pp. 32 and 33, (1977); U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, June 1978, pp. 9 to 15 (RD-17029).
Many processes have been proposed for obtaining color images. As to a process of forming color image by binding an oxidation product of a developing agent with a coupler, U.S. Pat. No. 3,531,286 has proposed p-phenylenediamine type reducing agents and phenolic or active methylene couplers, U.S. Pat. No. 3,761,270 has proposed p-aminophenol type reducing agents, Belgian Pat. No. 802,519 and Research Disclosure, September 1975, pp. 31 and 32 have proposed sulfonamidophenol type reducing agents, and U.S. Pat. No. 4,021,240 has proposed a combination of sulfonamidophenol type reducing agent and 4-equivalent coupler.
Also, processes for forming positive color images by a light-sensitive silver dye bleaching process, useful dyes and bleaching processes are described, for example, in Research Disclosure, April 1976, pp. 30 to 32 (RD-14433); ibid., December 1976, pp. 14 and 15 (RD-15227), and U.S. Pat. No. 4,235,957.
European Patent Application Nos. 76,492A and 79,056A, and Japanese Patent Application (OPI) Nos. 28928/83 and 26008/83 (the term "OPI" as used herein refers to a "Published unexamined Japanese patent application"), disclose an image-forming process by heat development utilizing a compound having a previously formed dye moiety and being capable of releasing a mobile dye at elevated temperatures corresponding to or inversely corresponding to reduction of silver halide to silver.
In these image-forming processes, alkali agents or alkali precursors are usually incorporated in light-sensitive materials for accelerating development upon heating. However, light-sensitive materials containing both a silver halide emulsion color-sensitized with a sensitizing dye and an alkali agent or an alkali precursor have a defect in that they tend to undergo a reduction in sensitivity during storage.
With the aforesaid system containing a compound having a previously formed dye moiety and being capable of releasing a mobile dye at elevated temperatures corresponding to or inversely corresponding to reduction of silver halide to silver, the use of a color-sensitized silver halide bring a particularly serious deterioration of preservability of light-sensitive materials. Since the dye-releasing compound itself has a dye moiety, the dye moiety may cause an interaction due to its dye properties with a sensitizing dye adsorbed on silver halide grains that have been color-sensitized with the sensitizing dye, such that the adsorbed sensitizing dye is desorbed from the surface of the silver halide grains during storage. This defect can be fatal with color light-sensitive materials and light-sensitive materials for electromagnetic waves of other regions than the intrinsic sensitivity region of silver halide.